pub fn cache_dir() -> Option<PathBuf>Expand description
Returns the directory the shared cache lives in, or None when no cache
location resolves. Honors $HARN_CACHE_DIR, then $XDG_CACHE_HOME/harn/bytecode,
then $HOME/.cache/harn/bytecode. The directory is not created here —
store creates it lazily on write so read-only environments don’t
pay an mkdir cost.